As raw materials for light-emitting device such as an ultraviolet, blue or green light-emitting diode as well as an ultraviolet, blue or green laser diode, there have been known group III-V compound semiconductors represented by the formula: InaGabAlcN (wherein a+b+c=1, 0≦a≦1, 0≦b≦1, 0≦c≦1). Hereinafter, a, b and c in the formula may be referred to as a mole fraction of InN, a mole fraction of GaN and a mole fraction of AlN, respectively. Among the group III-V compound semiconductors, those having an InN mole fraction of 5% or more are particularly important in applications for display, because they allow adjustment of wavelength of emitted light within the visible light region depending on the mole fraction of InN.
Although an attempt to grow a group III-V compound semiconductor layer on substrate such as sapphire, GaAs, ZnO and the like has been made, no crystals having a sufficiently high quality have been obtained, due to the fact that its lattice constant and chemical property are considerably different from those of the compound semiconductor. Therefore, an attempt to obtain an excellent crystal has been made by growing the compound semiconductor on GaN, which has lattice constant and chemical property similar to those of the compound semiconductor (JP-B-1980-3834).
In addition, although it is reported that a light-emitting device having a high efficiency can be obtained by forming a quantum well structure including a semiconductor represented by the formula: InaGabAlcN (wherein a+b+c=1, 0<a<1, 0<b<1, 0≦c<1)(JP 3,064,891), it is not always sufficiently acceptable in brightness.
Further, there has been known another process for producing a semiconductor, in which an InGaN layer is grown on a Si-doped GaN at 660 to 780° C., a GaN is grown after an interrupting growth for 5 to 10 seconds, the InGaN layer and GaN are repeatedly grown under such condition to form a multiple quantum well structure, and then a p-GaN layer is grown at 1040° C. It has also been known, however, that the InGaN layer is destructed during growing the p-GaN layer and In metal are deposited, thereby resulting significant decrease in brightness (Journal of Crystal Growth, 248, page 498 (2003))